Monitoring files - how to know when a file is complete

Question

We have several .NET applications that monitor a directory for new files, using FileSystemWatcher. The files are copied from another location, uploaded via FTP, etc. When th

Answer 1

The way I check in Windows if a file has been completely uploaded by ftp is to try to rename it. If renaming fails, the file isn't complete. Not very elegant, I admit, but it works.

Answer 2

The "Changed" event on the FileSystemWatcher should shouldn't fire until the file is closed. See my answer to a similar question. There is a possibility that the FTP download mechanism closes the file multiple times during download as new data comes in, but I would think that is a little unlikely.

Answer 3

You probably have to go with some out of band signaling: have the producer of "file.ext" write a dummy "file.ext.end".

Answer 4

Have you tried getting a write lock on the file? If it's being written to, that should fail, and you know to leave it alone for a bit...

Answer 5

A write lock doesn't help if the file upload failed part way through and the sender hasn't tried resending (and relocking) the file yet.

Answer 6

The following method tries to open a file with write permissions. It will block execution until a file is completely written to disk:

/// <summary>
/// Waits until a file can be opened with write permission
/// </summary>
public static void WaitReady(string fileName)
{
    while (true)
    {
        try
        {
            using (System.IO.Stream stream = System.IO.File.Open(fileName, FileMode.Open, FileAccess.ReadWrite, FileShare.ReadWrite))
            {
                if (stream != null)
                {
                    System.Diagnostics.Trace.WriteLine(string.Format("Output file {0} ready.", fileName));
                    break;
                }
            }
        }
        catch (FileNotFoundException ex)
        {
            System.Diagnostics.Trace.WriteLine(string.Format("Output file {0} not yet ready ({1})", fileName, ex.Message));
        }
        catch (IOException ex)
        {
            System.Diagnostics.Trace.WriteLine(string.Format("Output file {0} not yet ready ({1})", fileName, ex.Message));
        }
        catch (UnauthorizedAccessException ex)
        {
            System.Diagnostics.Trace.WriteLine(string.Format("Output file {0} not yet ready ({1})", fileName, ex.Message));
        }
        Thread.Sleep(500);
    }
}

(from my answer to a related question)